The goal of this research is to develop a structural basis for describing the solubility of small hydrophobic molecules in lipid bilayer membranes. Three fundamental questions are being asked: (1) When hydrophobic molecules dissolve in lipid bilayers, how are they distributed across the thickness of the bilayer? (2) How does the distribution vary with concentration? (3) How do structural changes in the hydrophobic molecules and the lipids of the bilayer affect the distribution? The answers to these questions form the basis for developing theories of the solubility of molecules in bilayers and may give important clues about molecular theories of solutions in general. This problem is important for understanding the organization of biological membranes and the molecular basis of anesthesia. Neutron diffraction will be used to construct neutron scattering density profiles of lipid multilayers deposited on quartz substrates in the presence and absence of small organic molecules such as alkanes, alcohols, and fluorocarbons. By carrying out the experiments first with non-deuterated organic molecules and then with deuterated organic molecules, the distribution of the molecules can be established unambiguously from difference Fourier Syntheses of neutron scattering density.